Various types of wheel brake control systems for vehicles are known. In most such systems, sensors are attached to the wheels of the vehicles which sense the speed of the wheel as well as the speed of the vehicle. Generally, a central control unit is provided which generates control commands which, in turn, adjust the braking pressure applied to the wheel brakes of the vehicles if predetermined driving or operating conditions obtain. Generally, control is effected in dependence on certain limiting values related to wheel acceleration or deceleration, respectively, and slippage between the wheel and the road or other support surface therefor. The publication "Bosch-Technische Berichte" ("Bosch-Technical Reports") describes such a system.
If the vehicle operates at extremely low speed, it is difficult to obtain suitable signals from the sensors coupled to the wheels, and particularly to obtain signals which can be evaluated with respect to slippage, acceleration or deceleration of the wheel. It has, therefore, been proposed to suppress automatic braking operation when the vehicle speed drops below a predetermined level. This level is related to the signals which can be processed by the anti-lock system--see, for example, German Patent Disclosure Document DE-OS No. 22 12 584. This system, thus, does not permit automatic braking at low vehicle speeds.